Medium optimization for the feather-degradation by Streptomyces fradiae Var S-221 using the response surface methodology

In order to accelerate biodegradation of feather into more amino acids, the fermentation medium of feather-biodegrading Streptomyces fradiae Var S-221 was optimized in this paper. In the first optimization step, the effects of feather powder, beet molasses, (NH4)(2)SO4 and KH2PO4 on amino acids formation were evaluated by using full factorial design. The results showed that feather powder and (NH4)(2)SO4 had significant and positive effects on feather-biodegradation into amino acids. Then, the method of the steepest ascent was used to access the optimal region of the two significant factors. In the third step, the concentration of feather powder and (NH4)(2)SO4 were further optimized with central composite design and response surface analysis. As a result, the composition of the optimal medium for S. fradiae Var S-221 fermentation were as follows (g/100 ml): feather powder, 19.504; beet molasses, 4.0; (NH4)(2)SO4, 1.467; KH2PO4, 0.3; MgSO4, 0.15; FeSO4, 0.001; ZnSO4, 0.0001; and MnSO4, 0.0001. Using this optimal fermentation medium, the amino acids concentration was increased from 4.61 to 6.13 g/100 ml.